This invention relates to the field of frothed urethane foams. More particularly, this invention relates to the process of curing mechanically frothed polyurethane foams and to polyurethane foams and laminates formed from mechanically frothed mixtures.
Mechanically frothed urethane foams have been developed and are known in the art for a variety of uses, including but not limited to carpet backing, coated fabrics and foam tapes. Such materials are typically processed by coating a foam layer onto a substrate or carrier and curing in a circulating air oven. Curing conditions for such foam materials are generally regarded as extreme, primarily because of the low thermal conductivity of the foams and resultant long times or high temperatures necessary to raise the temperature of the entire body of foam to the level necessary to effect cross-linking of the polymer. Thus, substantial energy inputs are required to effect the desired cure in circulating air ovens, and this typical prior art curing system has been very inefficient from an energy standpoint. In addition, it has been difficult to maintain accurate gauge control when processing thick layers (on the order of 0.25 inches or more) of mechanically frothed foam, particularly when forming foam-fabric laminates; and the formation of an integral skin on one side of the cured foam material has not been practicable with prior art techniques. The reliance on convection heating in circulating air curing ovens has resulted in an extremely inefficient and expensive curing process for these foam materials. In addition, slow curing rates have also contributed to inefficient curing operations.
Gauge control of foam sheets has also been a recurring probelm in the prior art. This problem has been particularly noticeable with foam-fabric laminates where the fabric layer in contact with the foam may be irregularly shaped. Such irregularities have tended to be perpetuated into the final product rather than being accommodated in a foam layer.
For many end uses of mechanically frothed polyurethane foam materials, it would be desirable to form an integral skin one one side of the foam, i.e. to form an integral high density exterior layer on one side of the foam. Such integral skin formation has been highly impracticable with prior art circulating air oven curing techniques.